Plot with extrapolation and interpolation

ROOT
1

Hi,

I have this 3 column data filedata_test.txt (274 Bytes) . I have plotted it using the following.

  TH3F *h3 = new TH3F("h3","3D",500,100,1000,500,500,1000,100,500,1000);
  for (unsigned i = 0; i < n; ++i) {
  in >> x >> y >> z;
  if (!in.good()) break;
  h3->Fill(x,y,z);
  }
  h3->Draw("cont4");

Now I want to have extrapolation and interpolation to get a smooth surface. Is there any way to do it?

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2

Have you tried the option ISO ?

3

Hi @couet, thanks.

No, I have not.
You meant,… instead of h3->Draw(“cont4”);, I should try h3->Draw(“GLISO”); ?

4

or just:

h3->Draw(“ISO”);

See the link I sent you.

5

And if I want to get a parametric equation out of it, then is there any option?

6

That’s not Drawing . May be have a look at 3D histogram fitting.

7 
h3->Draw(“ISO”); is creating something like this...not a colored surface.!
8

c1
c1.png698×327 7.27 KB

9

Yes, it is mono color. See the Help.
Try GLISO (with SetCanvasPreferGL before. See Help)
Also see if one of the examples here https://root.cern/doc/master/group__tutorial__gl.html
matches what you are looking for.

10

I have tried with GLISO also, but, didn’t work.

11

It might be there too less points to draw a surface through them using the available floating options. May be try to do a 3D fit.

12

Yeah, may be because of less data points…

But, how to do a 3D fit and get an equation back?

13
14

Thanks for the link. it is running. But, When I combine this with the one I posted at the beginning of this series, it does not show up in the plot and does not give the equation as well!

//file fit3.C
#include "TRandom3.h"
#include "Riostream.h"
#include <iostream>
#include "TH3.h"
#include "TF3.h"
#include "TMath.h"
   
double myfunc3(double *x, double *par) {
   double xx = (x[0] - par[1])/par[2];
   double yy = (x[1] - par[3])/par[4];
   double zz = (x[2] - par[5])/par[6];
   double rx = TMath::Exp(-xx*xx);
   double ry = TMath::Exp(-yy*yy);
   double rz = TMath::Exp(-zz*zz);
   double result = par[0]*rx*ry*rz;
   return result;
}
void fit3() {

   const unsigned nPts1 = 15; 
   ifstream in1;
   in1.open("data_test.txt");

   Float_t x1,y1,z1;

   TCanvas *c1 = new TCanvas("c1"," ",0,0,700,350);

   TH3F *h1 = new TH3F("h1","h1",100,1000,3000,100,0.5,1.0,100,0.0,1.0);

      for (unsigned i = 0; i < nPts1; ++i) {
      in1 >> x1 >> y1 >> z1;
      if (!in1.good()) break;
      h1->Fill(x1,y1,z1);
      }

   in1.close();

   c1->cd();
   TF3 *func3 = new TF3("func3",myfunc3,1000,3000,0.5,1.0,0.0,1.0,7);
   func3->SetParameters(h1->GetMaximum(),0,0.5,0,0.5,0,0.5);
   h1->Fit(func3,"r+","E");

   h1->Draw("col");
   func3->Draw("same");
   func3->SetLineColor(kOrange+8);
   func3->SetLineStyle(1);
   func3->SetLineWidth(2);
   h1->SetMarkerStyle(20);
   h1->SetMarkerSize(1.0);
   h1->SetMarkerColor(kBlue);

   c1->Update();
}
15

It gives me:

root [0] 
Processing fit3.C...
Warning in <Fit>: Fit data is empty

do you get the same ?

16

I am not getting any fit.

17

I got that but when you run the macro do you also get the message:

Warning in <Fit>: Fit data is empty
18

No…I am not getting that…:thinking:

19

here is the macro and the data i am using.
data_test.txt (274 Bytes) fit3.C (1.2 KB)

20

data_test.txt (227 Bytes)

If you test with this one, may be you can run: [please make changes correspondingly like following]

TH3F *h1 = new TH3F(“h1”,“h1”,100,1000,3000,100,0.5,1.0,100,0.0,1.0);

…
TF3 *func3 = new TF3(“func3”,myfunc3,1000,3000,0.5,1.0,0.0,1.0,7);